CEREAL IMPROVEMENT SELECTION 195 



199. Views of De Vries and Johannsen. Nothing 

 could appear more opportune than the expression of the 

 views of Hugo De Vries (1901-3) and W. Johannsen 

 (1903), simultaneously with the operations at Svalof. 

 These views, which appear to be rather generally, though 

 slowly, accepted, have served, together with the re- 

 discovery of Mendel's Law (see 217), to place the en- 

 tire phenomena of variation and development in a new 

 light 



The main principle in the views of De Vries is that of 

 the existence of " elementary species," an unfortunate 

 wording, referring to the types actually separated origi- 

 nally by Le Couteur and Shirreff and later by Nilsson 

 and associates. These " elementary species " or types 

 are unchangeable, in any permanent way, except through 

 occasional sudden variation's or " mutations" or by 

 hybridization. Even these processes do not change the 

 composition of the type, but add to or effect a recombina- 

 tion of the " unit characters " of which the type is com- 

 posed (220). 



200. Immutability of pure lines. Johannsen showed 

 the scientific necessity of working with pure lines by 

 which he meant the progeny of a single self-fertilizing 

 individual. The constituents of all his pure lines showed 

 fluctuations, it is true, in different directions, but when 

 some of these constituents which deviated to the farthest 

 extreme, were selected and propagated separately, instead 

 of producing a progeny similar to the mother plant, they 

 reverted to the original type of the line. Further experi- 

 ments finally forced Johannsen to conclude that con- 

 tinuous selection with pure lines cannot produce per- 

 manent changes, and that there is no hereditary variation 

 within pure lines. 



